From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 04F623B27DF for ; Thu, 11 Jun 2026 14:51:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781189494; cv=none; b=fmBj7CmKt0rbRxx4ItbaggC8CuylF8URTS2YhyVYloQ5NLruYpUSvV58fnTNLRADtiBl1zXsLZqhs3gKcEzB4NWyiLs8AQLWopEU3N4xk8kIhUYFaTDbJQJQqZ/2DCYOiAC6W9e+EbdfjFaaNJKTZJjlrn2f2hrb4yrfFF8knz8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781189494; c=relaxed/simple; bh=A7fU4LmkiZqHlzam0PtixzHFSmv7SqvsxdhZrNJlTiI=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=C9AS2k3UA4KCrlChdwzeCnMsrFsAuVq2GcFy7CYoDp4G3/A0ZJBFdPHsAMrL6ar3mJth/9G8u+yTufGpDxiRbSNAyBckajzHlRRdaPw1N5LI9RVVWCEuIHsyN3lJn1wgOmwPqnvgjm7Dxd3Yj6Ymj45+RkeGecGmQuFq/UMV2TY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=uYAF7xOs; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="uYAF7xOs" Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 1EFDC2661; Thu, 11 Jun 2026 07:51:27 -0700 (PDT) Received: from [192.168.1.148] (usa-sjc-mx-foss1.foss.arm.com [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id DF1053FD88; Thu, 11 Jun 2026 07:51:29 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1781189491; bh=A7fU4LmkiZqHlzam0PtixzHFSmv7SqvsxdhZrNJlTiI=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=uYAF7xOscmn2ISAlk4HMx7PU3T2t6cyEa6MW5v4v6BLCAxal9zT14FF18YsmwEP/i acyCo9+YYSAF+GEt6IkbPLOy/s5yXfqlG3+RikAQ+zY5tUzlkon7Mqjm4E+1JFHt+x HC/88TKJSFTiC8KN8/HRnbnXZOnjL5JaMKX0o9dE= Message-ID: Date: Thu, 11 Jun 2026 15:51:28 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v2 0/4] arm64: realm: Support for probing RSI earlier Content-Language: en-GB To: Catalin Marinas Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, will@kernel.org, ardb@kernel.org, lpieralisi@kernel.org, mark.rutland@arm.com, steven.price@arm.com, aneesh.kumar@kernel.org, sudeep.holla@arm.com, robh@kernel.org, maz@kernel.org References: <20260505155742.623287-1-suzuki.poulose@arm.com> <470678cb-b8b0-4b09-bf32-97fb037ed849@arm.com> From: Suzuki K Poulose In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 11/06/2026 12:14, Catalin Marinas wrote: > On Fri, May 29, 2026 at 01:27:01PM +0100, Suzuki K Poulose wrote: >> On 28/05/2026 17:06, Catalin Marinas wrote: >>> On Tue, May 05, 2026 at 04:57:38PM +0100, Suzuki K Poulose wrote: >>>> This is an updated series, addressing the review comments from AI agent on >>>> the version 1 [0] of the series, (some of which were documented as short comings). >>>> See below for the changes. >>>> >>>> The Realm Guest linux support is broken without rodata=full (fortunately default >>>> for arm64), as we detect the RSI support after we have created the Linear map >>>> with Block/Contiguous mappings. If the boot CPU doesn't support BBML2_NOABORT >>>> (there are CPUs out there with FEAT_RME and no - useable - BBML2_NOABORT) >>>> we are then not able to split the page tables down to PTE level if the system >>>> as such doesn't support BBML2. >>>> >>>> See the following link for the discussion. >>>> >>>> https://lore.kernel.org/all/20260330161705.3349825-2-ryan.roberts@arm.com/ >>>> >>>> The available options are : >>>> 1. Start with PTE level mappings at paging_init() and then "FOLD" the page tables >>>> to Block/Cont mappings after we have the full picture available. Looking at the >>>> future (with BBML3), this might mean "additional work" for most of the systems >>>> at boot. But not bad as splitting them ? >>>> 2. Hold the secondary CPUs in busy loop with MMU disabled and split the mappings >>>> by the boot CPU with MMU off (if Boot CPU can't support BBML2). This is tricky >>>> with the page allocations required to add the page-tables. >>>> 3. Move the detection of Realm support earlier to make a better decision for >>>> paging_init(), with an added bonus of earlycon support for Realms without >>>> the user having to work out the "top bit" for the Realm. >>>> >>>> This series is an attempt to implement (3) (without the earlycon support). We try >>>> to probe the PSCI conduit early from the DT/ACPI. DT is not flattened at this time. > [...] >>> Could we instead add a more informative message in arm64_rsi_init() if >>> !force_pte_mappings() && !cpu_supports_bbml2_noabort() (before >>> is_realm_world() becomes true)? Well, it may not print anything if the >>> early console is not set up yet. >> >> That is true, but with some expertise you may be able to enable earlycon >> and may be we could get some new mechanism for "earlycon" for Realms. >> >> The other way to look at is: >> >> When the system doesn't support BBML2 Abort: >> >> Creating block/Cont mappings to start with and then splitting it to PTE >> is quite difficult as we : >> 1. Need to allocate pages for leaf level tables >> 2. Hold the other CPUs in tight loop > > Agree, that's not easily possible at runtime. > >> Instead, creating the block/CONT levels from a fully "page level" >> mappings are easier, as we can: >> >> 1. Can easily fold the tables to Block mapping with reclaiming the leaf >> level pagetables. >> >> 2. Avoid the secondary CPUs dance, as they all support BBML2_NOABORT. >> >> This shouldn't be that bad as the opposite ? > > I don't think it solves our problem. Aren't we concerned with the > rodata=off && !BBML2_NOABORT && is_realm_world() case? I don't think > your second point stands. > > Currently we have: > > rodata=full && BBML2_NOABORT => block mappings irrespective of realms > > rodata=off && BBML2_NOABORT => block mappings first, can be split later > if is_realm_world() > > rodata=off && !BBML2_NOABORT => block mappings first, serious problem if > is_realm_world() > > It's the last case we need to fix. Starting with page mappings does > avoid the in-realm failure but the !is_realm_world() case folding to > block mappings still requires proper BBM. I see, the case I was missing is : !is_realm_world() and !BBML2_NO_ABORT and we want Block mapping if rodata=off. Yes, in this case we need the secondaries on hold, with proper BBM on the boot CPU too. Again, it is easier to "collapsing the tables to Block" than the reverse. Suzuki >